1. Technical Field
The present invention relates to an indication member that serves as an object to be detected at a position detection time, an optical position detection device having the indication member, and a display system including the position detection device.
2. Related Art
A known optical position detection device for optically detecting a target object includes a light receiving section provided at a position separated from a plurality of light source sections. When detection light is emitted from the plurality of light source sections toward a target object through a light transmissive member, detection light reflected from the target object is transmitted through the light transmissive member and is then detected by the light receiving section (refer to JP-T-2003-534554). Another known optical position detection device directs detection light emitted from a plurality of light source sections through a light guide plate. Detection light reflected from a target object is then detected by a light receiving section (refer to JP-A-2010-127671 and JP-A-2009-295318). In this optical position detection device, the position of the target object is detected by comparing the received light intensity in the light receiving section when some of the light source sections are lit with the received light intensity in the light receiving section when other light source sections are lit.
In the optical position detection devices disclosed in JP-T-2003-534554, JP-A-2010-127671, and JP-A-2009-295318, however, there is a problem in that the received light intensity in the light receiving section is low. This is because detection light that is scattered or diffusely reflected by the target object is received by the light receiving section. As a result, the detection accuracy is low. Further, even if a portion for regular (non-scattered and non-diffused) reflection is provided in the target object to solve such a problem, the received light intensity in the light receiving section is only significantly reduced if the target object is appropriately positioned. Accordingly, it is difficult to improve detection accuracy.
One proposal for improvement involves an indication member that has a round bar portion at its distal end so that the outer peripheral surface thereof serves as a retroreflective portion (refer to JP-A-2011-14107). With this indication member, detection light emitted from a light source section of an optical unit is reliably reflected from the retroreflective portion of the indication member and is then incident on a light receiving section of the optical unit. Therefore, there is an advantage in that the received light intensity in the light receiving section is high.
With the indication member disclosed in JP-A-2011-14107, however, position detection is performed on the basis of light reflected from the entire round bar portion serving as the retroreflective portion. For this reason, when the indication member is inclined, an intermediate part of the round bar portion in the longitudinal direction may be erroneously detected as an indication position even though the distal end of the round bar portion is at the indication position. Since the round bar portion cannot be elongated, there is a problem in that the effect of increasing the received light intensity in the light receiving section is small and detection accuracy cannot be sufficiently improved.